This invention relates to a grain dryer and is particularly useful for the preliminary drying of rice and corn. Many grains require preliminary drying before processing. This enables the grain that is handled in subsequent steps to have a preliminarily lowered moisture content that both protects and preserves the grain during handling and transport to subsequent steps that may vary for different resulting products. For example, treatment steps for use of grain in prepackaged food may differ substantially from those used in canned or other precooked preparations. Before commencing selected processing steps, bulk grains should be uniformly dried to create a protective outer surface to lock in nutrients and flavoring and to assist in toughening the grain for bulk handling.
The step of preliminary drying is generally accomplished at large granaries where massive quantities of grain are treated, stored and shipped. In the conventional vertical drier, a large central plenum, that may be many stories in height, is continuously filled with hot air that escapes through a double-layer wire mesh skin, between which the grain is dropped. As the hot air escapes to the outside, the grain dries as it cascades down between the mesh screens. In general, the mesh screens in the sheath are spaced approximately one foot apart. It has been found that grain dropping between the mesh screens do not substantially mix and that substantially all of the drying is accomplished in the first two to three inches of depth into the decending grain.
The exterior grain is inadequately dried by the dramatically falling air temperature as the air passes through the grain from the inner plenum to the outer atmosphere. Furthermore, overdrying of grain, particularly rice, can cause damage including rupture of the hull rendering the rice less desirable for food processing and suitable for normal feed or mash for alcoholic beverages food fillers or animal feed. In a conventional vertical drier, the lack of mixing results in the stream of feed grain closest to the internal plenum to be overdried and the grain stream closest to the outside atmosphere underdried, such that a substantial lack of uniformity in moisture content occurs. Customarily, this is partially resolved by repeatedly cycling the grain through the vertical drier to achieve the approximate overall consistency and uniformly in moisture contend desired. Individual grains may be overdried and underdried by this averaging method.
The inefficiencies in drying and the requirement of recycling for redrying results substantial wastes in electrical energy and thermal energy. Furthermore, the repeated handling of the grain adds to kernal damage and still does not achieve the consistency in drying that is most desirable for production of premium bulk grain.
These and other problems with existing driers have led to development of an improved drier that allows drying of grain to desired moisture content in a single pass. The improved dryer further accomplishes the drying with an energy savings of approximately one third of the usual energy costs. These and other improvements will become apparent from a consideration this invention in the detailed description of the preferred embodiment.